Hybrid Ultrathin Gold Nanowire Gels: Formation and Mechanical Properties.

This report is about the chemical formation of gels from ultrathin gold nanowires (AuNWs) and the gels' properties. An excess of triphenylphosphine (PPh) initiated the gelation of AuNWs with core diameters below 2 nm and an oleylamine (OAm) ligand shell dispersed in cyclohexane. The ligand exchange of OAm by PPh changes the AuNW-solvent interactions and leads to phase separation of the solvent to form a macroscopic gel.

Synthesis and Self-Assembly of Pore-Forming Three-Arm Amphiphilic Block Copolymers.

The synthesis of an amphiphilic three-arm block copolymer (AB)-BCP, which consists of poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA) in the hydrophobic inner block, is reported. The hydrophilic block segment is based on poly(2-hydroxyethyl methacrylate) (PHEMA) originating from 2-(trimethylsiloxyl)ethyl methacrylate (HEMA-TMS). The preparation is carried out in two steps using a core-first approach.

Near-Infinite-Chain Polymers with Ge=Ge Double Bonds.

Despite considerable interest in heteroatom-containing conjugated polymers, there are only few examples with heavier p-block elements in the conjugation path. The recently reported heavier acyclic diene metathesis (HADMET) allowed for the synthesis of a polymer containing Ge=Ge double bonds-albeit insoluble and with limited degree of polymerization. By incorporation of long alkyl chains, we now obtained soluble representatives, which exhibit degrees of polymerization near infinity according to diffusion-ordered NMR spectroscopy (DOSY) and dynamic light scattering (DLS).

PNIPAM Mesoglobules in Dependence on Pressure.

Poly(-isopropylacrylamide) (PNIPAM) in aqueous solution forms mesoglobules above its cloud point temperature . While these are small and compact at atmospheric pressure, they are large and water-rich at high pressure. To identify the transition between these states, we employed optical microscopy and carried out isothermal pressure scans.

Stabilization of Apolar Nanoparticle Dispersions by Molecular Additives.

We study the effect of additives on the colloidal stability of alkanethiol-coated gold nanoparticles. Cyclic amines and sulfides of different sizes were added to dispersions in decane at additive concentrations below 128 mM. Small-angle X-ray scattering (SAXS) indicated that tetrahydrothiophene reduced the agglomeration temperature, , by up to 29 °C, a considerable increase in colloidal stability.

Catalyst Supraparticles: Tuning the Structure of Spray-Dried Pt/SiO Supraparticles via Salt-Based Colloidal Manipulation to Control their Catalytic Performance.

The structure of supraparticles (SPs) is a key parameter for achieving advanced functionalities arising from the combination of different nanoparticle (NP) types in one hierarchical entity. However, whenever a droplet-assisted forced assembly approach is used, e.g.

Thermoresponsive Polymers under Pressure with a Focus on Poly(-isopropylacrylamide) (PNIPAM).

Pressure is a key variable in the phase behavior of responsive polymers, both for applications and from a fundamental point of view. In this feature article, we review recent developments, particularly applications of neutron techniques such as small-angle neutron scattering (SANS) and quasi-elastic neutron scattering (QENS), across the temperature-pressure phase diagram. These are complemented by kinetic SANS experiments following pressure jumps.

Self-Healing Iron Oxide Polyelectrolyte Nanocomposites: Influence of Particle Agglomeration and Water on Mechanical Properties.

Self-healing nanocomposites can be generated by organic functionalization of inorganic nanoparticles and complementary functionalization of the polymer matrix, allowing reversible interactions between the two components. Here, we report on self-healing nanocomposites based on ionic interactions between anionic copolymers consisting of di(ethylene glycol) methyl ether methacrylate, sodium 4-(methacryloyloxy)butan-1-sulfonate, and cationically functionalized iron oxide nanoparticles. The materials exhibited hygroscopic behavior.

Self-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers.

The fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene--poly(methyl methacrylate) block copolymer (PS--PMMA) was synthesized through anionic polymerization.

Bifunctional Carbanionic Synthesis of Fully Bio-Based Triblock Structures Derived from β-Farnesene and ll-Dilactide: Thermoplastic Elastomers.

Current environmental challenges and the shrinking fossil-fuel feedstock are important criteria for the next generation of polymer materials. In this context, we present a fully bio-based material, which shows promise as a thermoplastic elastomer (TPE). Due to the use of β-farnesene and L-lactide as monomers, bio-based feedstocks, namely sugar cane and corn, can be used.

The Colloidal Stability of Apolar Nanoparticles in Solvent Mixtures.

Solvent engineering is a powerful and versatile method to tune colloidal stability. Here, we link the molecular structure of apolar ligand shells on gold nanoparticles with their colloidal stability in solvent mixtures. The agglomeration temperature of the particles was measured with small-angle X-ray scattering.

Surface polarization, field homogeneity, and dielectric breakdown in ordered and disordered nanodielectrics based on gold-polystyrene superlattices.

Hybrid dielectrics were prepared from dispersions of nanoparticles with gold cores (diameters from 2.9 nm to 8.2 nm) and covalently bound thiol-terminated polystyrene shells (5000 Da and 11 000 Da) in toluene.

Cononsolvency of thermoresponsive polymers: where we are now and where we are going.

Cononsolvency is an intriguing phenomenon where a polymer collapses in a mixture of good solvents. This cosolvent-induced modulation of the polymer solubility has been observed in solutions of several polymers and biomacromolecules, and finds application in areas such as hydrogel actuators, drug delivery, compound detection and catalysis. In the past decade, there has been a renewed interest in understanding the molecular mechanisms which drive cononsolvency with a predominant emphasis on its connection to the preferential adsorption of the cosolvent.

Droplet Formation by Chemically Fueled Self-Assembly: The Role of Precursor Hydrophobicity.

We investigate active droplets that form at the expense of a chemical fuel in aqueous buffer and vanish autonomously. Dynamic light scattering reveals the scattered intensity, the hydrodynamic radius, and the width of the size distribution with high precision as well as high temporal and spatial resolutions. Comparing the resulting time-dependent behavior of the droplet characteristics with the time-dependent concentration of the anhydrides, the roles of the chemical reaction cycle and of colloidal growth processes are elucidated.

An Outer Membrane Vesicle-Based Permeation Assay (OMPA) for Assessing Bacterial Bioavailability.

When searching for new antibiotics against Gram-negative bacterial infections, a better understanding of the permeability across the cell envelope and tools to discriminate high from low bacterial bioavailability compounds are urgently needed. Inspired by the phospholipid vesicle-based permeation assay (PVPA), which is designed to predict non-facilitated permeation across phospholipid membranes, outer membrane vesicles (OMVs) of Escherichia coli either enriched or deficient of porins are employed to coat filter supports for predicting drug uptake across the complex cell envelope. OMVs and the obtained in vitro model are structurally and functionally characterized using cryo-TEM, SEM, CLSM, SAXS, and light scattering techniques.

Nanoscale disintegration kinetics of mesoglobules in aqueous poly(N-isopropylacrylamide) solutions revealed by small-angle neutron scattering and pressure jumps.

Identification and control of the disintegration mechanism of polymer nanoparticles are essential for applications in transport and release including polymer delivery systems. Structural changes during the disintegration of poly(N-isopropylacrylamide) (PNIPAM) mesoglobules in aqueous solution are studied in situ and in real time using kinetic small-angle neutron scattering with a time resolution of 50 ms. Simultaneously length scales between 1 and 100 nm are resolved.

Co-nonsolvency in concentrated aqueous solutions of PNIPAM: effect of methanol on the collective and the chain dynamics.

The polymer dynamics in concentrated solutions of poly(N-isopropyl acrylamide) (PNIPAM) in D2O/CD3OD mixtures is investigated in the one-phase region. Two polymer concentrations (9 and 25 wt%) and CD3OD contents in the solvent mixture of 0, 10 and 15 vol% are chosen. Temperature-resolved dynamic light scattering (DLS) reveals the collective dynamics.

Formation and Growth of Mesoglobules in Aqueous Poly(-isopropylacrylamide) Solutions Revealed with Kinetic Small-Angle Neutron Scattering and Fast Pressure Jumps.

The phase transition from swollen chains to polymer mesoglobules of an aqueous solution of poly(-isopropylacrylamide) is investigated with kinetic small-angle neutron scattering with 50 ms time resolution in conjunction with millisecond pressure jumps across the coexistence line. The time-resolved study evidenced three distinct regimes: fractal clusters form during the first second and transform into compact mesoglobules. During the following ∼20 s, these grow by diffusion-limited coalescence.

Polysulfobetaines in Aqueous Solution and in Thin Film Geometry.

Polysulfobetaines in aqueous solution show upper critical solution temperature (UCST) behavior. We investigate here the representative of this class of materials, poly (,-dimethyl--(3-methacrylamidopropyl) ammonio propane sulfonate) (PSPP), with respect to: (i) the dynamics in aqueous solution above the cloud point as function of NaBr concentration; and (ii) the swelling behavior of thin films in water vapor as function of the initial film thickness. For PSPP solutions with a concentration of 5 wt.

Macromolecular pHPMA-Based Nanoparticles with Cholesterol for Solid Tumor Targeting: Behavior in HSA Protein Environment.

Nanoparticles (NPs) that form by self-assembly of amphiphilic poly(N-(2-hydroxypropyl)-methacrylamide) (pHPMA) copolymers bearing cholesterol side groups are potential drug carriers for solid tumor treatment. Here, we investigate their behavior in solutions of human serum albumin (HSA) in phosphate buffered saline. Mixed solutions of NPs, from polymer conjugates with or without the anticancer drug doxorubicin (Dox) bound to them, and HSA at concentrations up to the physiological value are characterized by synchrotron small-angle X-ray scattering and isothermal titration calorimetry.

Pressure-Dependence of Poly(-isopropylacrylamide) Mesoglobule Formation in Aqueous Solution.

Above their cloud point, aqueous solutions of the thermoresponsive polymer poly(-isopropylacrylamide) (PNIPAM) form large mesoglobules. We have carried out very small-angle neutron scattering (VSANS with = 0.21-2.

pH Responsiveness of hydrogels formed by telechelic polyampholytes.

We investigate the influence of pH on the rheological and structural properties of hydrogels formed by hydrophobic association of the sticky ends of the triblock terpolymer poly(methyl methacrylate)-b-poly(2-(diethylamino)ethyl methacrylate-co-methacrylic acid)-b-poly(methyl methacrylate) (PMMA-b-P(DEA-co-MAA)-b-PMMA). The middle block is a weak polyampholyte having a pH dependent charge density and sign, which enables tuning of the rheological and structural properties by pH variation. Small-angle neutron scattering (SANS) studies of solutions in DO at 0.